Keypad pcb assembly for mobile phone with light guide plate

ABSTRACT

A keypad printed circuit board (PCB) assembly for a mobile phone integrated with a light guide plate providing a light-emitting function using a light emitting diode (LED) and the light guide plate is provided. The keypad PCB assembly includes a PCB on which a plurality of light emitting diodes (LEDs) is surface-mounted such that they are able to light-emit from a side of the PCB, a metal dome section including metal dome parts attached to positions corresponding to signal contacts of the PCB, and a dome tape covering a gap between the metal dome parts excluding a portion overlapped with the LEDs, and a light guide plate coupled to an upper portion of the metal dome section so that the light guide plate and the metal dome section are integrated into one piece, leaving the space therebetween, and having thereunder an uneven pattern reflecting light incident from the LEDs, an LED cover provided on a position corresponding to the LEDs, and a circumferential light-shielding part filling the end-side space between the light guide plate and the metal dome section.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a keypad printed circuit board (PCB)assembly for a mobile phone, and more particularly to a keypad PCBassembly for a mobile phone integrated with a light guide plateproviding a light-emitting function using a light emitting diode (LED)and the light guide plate.

2. Description of Prior Art

As generally known in the art, a light-emitting device of a keypad for amobile phone is mainly a light-emitting diode (LED) type, but recently,there has been a trend towards distributing an electroluminescence (EL)type in high-cost models.

The LED type is a type in which LEDs are surface-mounted to manypositions (e.g., 10 to 20 points) on a keypad to illuminate the whole ofthe keypad. Such an LED type has problems in that due to using so manyLEDs, high power consumption is caused to shorten the lifetime of abattery, and in view of light-emitting, a difference in luminance occursdepending upon near-far effect from the LEDs, causing inhomogeneity inlight-emitting.

The EL type is realized as an EL sheet having high power saving, superthinning, and homogeneous light-emitting features, and is thusspotlighted. However, the EL type has problems in that noises occur dueto electrical interference, and it needs a high cost driving circuit,thereby increasing production costs.

Further, while there is an attempt to improve the quality oflight-emitting by adapting a light guide plate for back light to amobile phone, there is not yet proposed a practical method ofmanufacturing a light-emitting assembly to solve the above problems aswell as to satisfy the objective light-emitting feature and easyproductivity.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve theabove-mentioned problems occurring in the prior art, and the presentinvention provides a keypad printed circuit board (PCB) for a mobilephone integrated with a light guide plate and using a light emittingdiode (LED) and a light guide plate while solving the problems of aconventional LED type structure, such as inhomogeneity in light emissionand higher power consumption. The keypad PCB has advantages of anelectroluminescence (EL)-type light emission structure, such as powersaving, super thinning, and homogeneous light-emission features withoutadopting the EL type structure having defects of high costs and noiseoccurrence.

In order to accomplish the above object, in accordance with an aspect ofthe present invention, there is provided a keypad printed circuit board(PCB) assembly for a mobile phone comprising: a PCB on which a pluralityof light emitting diodes (LEDs) is surface-mounted such that they areable to light-emit from a side of the PCB; a metal dome sectionincluding metal dome parts attached to positions corresponding to signalcontacts of the PCB and a dome tape covering a gap between the metaldome parts excluding a portion overlapped with the LEDs; and a lightguide plate coupled to an upper portion of the metal dome section sothat the light guide plate and the metal dome section are integratedinto one piece, leaving the space therebetween, and having thereunder anuneven pattern reflecting light incident from the LEDs, an LED coverprovided on a position corresponding to the LEDs, and a circumferentiallight-shielding part filling the end-side space between the light guideplate and the metal dome section.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a exploded perspective view of a keypad light-emitting printedcircuit board (PCB) assembly according to the present invention;

FIG. 2 is a plan view of the keypad light-emitting PCB assembly (a firstembodiment) according to the present invention;

FIG. 3 is a sectional view taken along line A-A′ of FIG. 2; and

FIG. 4 is a plan view of the keypad light-emitting PCB assembly (asecond embodiment) according to the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Hereinafter, an exemplary embodiment of the present invention will bedescribed with reference to the accompanying drawings. In the followingdescription and drawings, the same reference numerals are used todesignate the same or similar components, and so repetition of thedescription on the same or similar components will be omitted.

FIG. 1 is an exploded perspective view of a keypad light-emittingprinted circuit board (PCB) assembly according to the present invention.The PCB assembly includes a printed circuit board (PCB), a metal domesection, and a light guide plate as named from the bottom.

The present invention relates to a keypad PCB for a mobile phone havinga light-emission function. The elements other than light-emissionfunction-related elements are the same as those of a conventional keypadfor a mobile phone, so the detailed explanation thereof will be omitted.

As for the PCB 1, a PCB adopted to an electroluminescence (EL) keypad ora flexible printed circuit board is generally used. On the PCB, lightemitting diodes (LEDs) 11 (preferably, two LEDs) capable of sidelight-emitting are mounted in series on the surface of the PCB along oneside (preferably, along the upper side) of the PCB so as to be apartfrom each other. Here, the side light-emitting LED includes an LEChaving a side view function or an LED capable of providing a sidelight-emitting function through a structural modification. In principle,the LED is enough so long as it can provide side light-emitting parallelwith a keypad.

The metal dome section 2 includes a metal dome parts 21 and a dome tape22, which are coupled to the upper side of the PCB. The metal dome partsare provided on positions corresponding to contact points between thekeypad and the PCB. The dome tape fills an uneven portion formed by themetal dome parts and covers the metal dome parts, thereby fixing themetal dome parts in place. The metal dome section may be generallyadopted from that of an EL keypad, but according to the presentinvention, a light guide plate instead of an EL sheet is coupled to themetal dome section so that the dome tape is coated with a reflectinglayer reflecting light without absorption so as to prevent light loss ofthe LED. Here, the coating is carried out over the whole dome tapeexcept a portion where the LEDs are located, so as to allow light fromthe LEDs to be directed toward the metal dome section.

The light guide plate 3 is a thin film contributing to light diffusion,and is generally made of transparent polycarbonate or rubber material.The light guide plate includes an uneven pattern 31, an LED cover 32,and a circumferential light-shielding part 33. The light guide plate iscoupled to the upper portion of the metal dome section, leaving thespace therebetween, so that LED light incident to the metal dome sectionfrom a side of the PCB is concentrated on the uneven pattern portionwhile remaining on specified portions (keys of the keypad) by the unevenpattern formed under the light guide plate.

The design of the uneven pattern 31 is an important factor influencingluminance or homogeneity of light, so that it has to be modified inaccordance with product design or a surface-mounting position of an LED.

That is, it is important to design the uneven pattern such that the sizeand the density of the pattern are modified in accordance with adistance from a light source and a light-emission angle. In FIG. 2, akey near the LED light source is designed to have a smaller, lowerpattern so as to allow light to pass through in great quantities, and akey far from the light source is designed to have a larger, densepattern considering a positional problem in that an absolute quantity oflight must be poor, so as to block light passage and preserve lighttherein in greater quantities.

The uneven pattern may be solely designed for each key depending on theshape of the key, or otherwise, it may be designed into a shape such asa stripe pattern denoted as a reference numeral 31 a covering aplurality of keys. FIG. 4 is an exemplary view of the PCB assembly inwhich the LEDs are surface-mounted on both upper edges of the keypad,and a stripe pattern is adopted as an uneven pattern of the light guideplate. Like this, it is possible to modify a surface-mounting positionof an LED and a shape of an uneven pattern into diverse types.

However, the most important point in designing an uneven pattern is tomaximize the efficiency of light transmission, which can be controlledby the density and height of the pattern due to a difference inbrightness, but in basic, a pattern-forming position should be an underface of the light guide plate. If a reflection pattern is formed on theupper portion of the light guide plate, light loss occurs so that lightguide effect is not realized normally. The reflection pattern may bemodified in various forms so long as it has the above function.

In addition, on the light guide plate, the LED cover 32 coated with areflection layer is installed on a position corresponding to an LEDposition so as to prevent light from being refracted and lost whilebeing directed upward the light guide plate. Furthermore, thecircumferential light-shielding part 33 is provided to fill the spacebetween the light guide plate and the dome section so as to preventlight from leaking through the side of the light guide plate.

FIG. 3 is a sectional view taken along line A-A′ of FIG. 2, in which theassembled state of the PCB, the metal dome section, and the light guideplate is shown. It is shown that the space between the light guide plateand the metal dome section is formed by the adhesion therebetween so asto allow light to be guided through the space.

The present invention relates to a technique of the keypad PCB for amobile phone integrated with the light guide plate, and provides thekeypad PCB in which the light guide plate is integratedly coupled to thePCB, on which a dome switch, a driving circuit, an LED, etc. aresurface-mounted, the light guide plate being provided with alight-reflection pattern to allow LED light to be directed through thepattern.

Such a structural difference makes it possible to incorporate theapplication of the light guide plate in a manufacturing process of thePCB, providing the effects of easy manufacturing and high productreliability. Moreover, the difference enables the technology of thelight guide plate satisfying both economy and functionality to beapplied to the keypad of a mobile phone successfully.

The present invention has significance for proposing a PCB structure anda manufacturing method thereof capable of securing stability of the LEDkeypad while providing a thinner, high power-saving structure like aconventional EL keypad on a basis of a technical idea of using the lightguide plate instead of an EL sheet.

Thus, among the elements adopted to the conventional keypad structure,some elements used in the present invention can be modified in variousforms, so that the technical scope of the present invention has to bedetermined taking the above fact into consideration, and it cannot beasserted that the modification in the portion corresponding to the priorart does not pertain to the present invention.

According to the present invention, as an improved technology of alight-emitting keypad PCB assembly, the structure and manufacturingmethod thereof capable of realizing a super thinning keypad like an ELkeypad, using the light guide plate and the LED are provided.

Although an exemplary embodiment of the present invention has beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A keypad printed circuit board (PCB) assembly for a mobile phonecomprising: a PCB on which a plurality of light emitting diodes (LEDs)is surface-mounted such that they are able to light-emit from a side ofthe PCB; a metal dome section including metal dome parts attached topositions corresponding to signal contacts of the PCB, and a dome tapecovering a gap between the metal dome parts excluding a portionoverlapped with the LEDs; and a light guide plate coupled to an upperportion of the metal dome section so that the light guide plate and themetal dome section are integrated into one piece, leaving the spacetherebetween, and having thereunder an uneven pattern reflecting lightincident from the LEDs, an LED cover provided on a positioncorresponding to the LEDs, and a circumferential light-shielding partfilling the end-side space between the light guide plate and the metaldome section.
 2. The keypad PCB assembly as claimed in claim 1, whereinthe uneven pattern of the light guide plate is solely formed accordingto a position of a key, or is formed in a stripe pattern covering aplurality of keys, the pattern being designed such that the size and thedensity of the pattern vary according to a distance from an LED lightsource.
 3. The keypad PCB assembly as claimed in claim 1, wherein twoLEDs are separately provided in series along an upper side of the PCB.4. The keypad PCB assembly as claimed in claim 1, wherein the dome tapeof the metal dome section is coated with a reflection layer reflectinglight upward.